"We would now have to advise any person who thinks they have an incorrect Centrelink debt that, if they speak publicly about their situation, their confidential information is no longer safe with Centrelink," he said.

Peter Sutherland, a social security legal expert at the Australian National University (ANU), said the department had never made a public disclosure with this specific legal argument.

"This appears to be a new practice," he said.

Privacy Commissioner Timothy Pilgrim has made inquiries with the department to determine whether any laws were broken.